I've encrypted my Dropbox folder with EncFS according to a few tutorials I found on the web, advocating this approach.
But I've found the following critical statement concerning EncFS's security in this security-audit:
EncFS is probably safe as long as the adversary only gets one copy of the ciphertext and nothing more. EncFS is not safe if the adversary has the opportunity to see two or more snapshots of the ciphertext at different times. EncFS attempts to protect files from malicious modification, but there are serious problems with this feature.
So, as long as they only get one copy of the encrypted files it's fine, but if they get more, it might be dangerous.
Well, when using Dropbox, they would get a hell lot of different snapshots of the encrypted files (since they will be synchronized after every change).
Thus EncFS would be not a secure solution in combination with a cloud-service à la Dropbox, right?